I. Field of the Invention
The present invention relates generally to the field of roadway manhole devices. More particularly, the present invention relates to a manhole extender ring system which vertically adjusts the top surface of a manhole cover to be flush with the roadway surface regardless of the grade.
II. Description of the Related Art
Roadways often cross telephone lines, electrical lines and various types of devices. Typically, maintenance workers gain access to these lines and devices via manholes. It is common for manholes to have a brick or concrete foundation with an annular, metallic support having a cover mounted to the foundation and embedded within the roadway surface. The cover generally is flush with the roadway surface to provide a smooth and safe passage for vehicles using the roadway. However, roadway surfaces have limited lifetimes due to climatic degradation and wear from vehicle use. Compensating for these effects, the roadways are periodically resurfaced, requiring the roadway workers to raise the support of the manhole unit to the new roadway surface level.
To raise the support it generally takes 2 to 4 workers several hours of labor to jackhammer out the roadway surface material, such as asphalt and concrete, around the support. Normally, the manhole is not raised until after the new roadway has been laid. This, of course, destroys a portion of the new roadway. Occasionally, portions of the foundation are removed. After the support has been removed, the foundation is raised by a height equivalent to the thickness of the new roadway surface with new bricks and/or mortar. The mortar is allowed to cure for a number of hours, requiring the use of barricades and sometimes the detouring of traffic.
There are many types of manhole support devices capable of modification to accommodate the addition of new roadway surfaces over old roadway surfaces. Several are described in U.S. Pat. Nos. 4,149,816, 4,273,467, 4,925,337, 5,205,668, 5,211,504, and 5,360,131.
Described in U.S. Pat. No. 3,773,428 by Bowman is an adjustable manhole cover support. The device has a frame and a peripheral manhole adjusting ring disposed on the frame. The ring is adjusted vertically and secured within the frame by set screws or spacers to raise or lower a manhole cover. The vertical adjustment is limited by the length of the set screws and a gap is created between the frame and the ring when the ring is adjusted away from the frame.
A height adjustable road manhole cover described in German Patent Number 30 16 401 by Lindner describes a topping piece with end face steps for mounting a lid and a holder for a lid-securing piece. A pair of compensating rings raise the vertical height of the holder and the lid. The holder is secured by use of set screws.
Described in U.S. Pat. No. 4,976,568 by Hess is a device for raising the level of a manhole cover. The device has a frame, a ring having a mounting surface adapt to sit on the top of the frame and a manhole cover. As with Bowman and Lindner, the ring is secured to the frame by set screws.
An adjustable manhole cover assembly described in U.S. Pat. No. 5,044,818 by Pritchard has an annular frame and an annular sleeve member repositioned so as to rest on a first annular adjustment ring to adjust the system to the desired height. The sleeve member is positioned within the frame and is secured by an outwardly projecting flange which is captured by the roadway surface.